Five Ukrainian government troops battling separatist forces in the east have been killed in one of the worst single days of bloodshed since a cease-fire was declared in February, military officials said Wednesday.

Army spokesman Andriy Lysenko said four soldiers died when their armored vehicle hit a mine near the front line town of Avdiivka. Another was killed in an ambush at another location, Lysenko said.

Skirmishes have reportedly increasing in recent weeks along the line of contact between the warring sides.

Some diplomatic effort was made Wednesday to reach a more enduring settlement as Ukrainian and separatist representatives met for talks in the Belarusian capital of Minsk.

The talks, under the auspices of the Organization for Security and Cooperation in Europe (OSCE), agreed to form so-called “subgroups'' of rebel and Ukrainian representatives to discuss political, security, economic and humanitarian matters.

The political group is likely to have the most challenging task as it discusses what degree of autonomy the rebel regions could have while remaining part of Ukraine.

“What was done today is a serious step toward political resolution; it will promote the halt of shooting,'' said Azamat Kulakhmetov, Russia's representative to the talks.

More than 6,000 people have died over a year of conflict fueled by an armed insurgency calling for the breakaway of Russian-speaking eastern Ukrainian regions.

International cease-fire monitors say both parties are violating the peace agreement by deploying heavy weapons near the front-line.

Separatists have been showing off large amounts of their hardware in rehearsal for a military parade to take place later this week in their stronghold of Donetsk. The city is only a few kilometers from the front-line, so deployment of any firepower with a caliber superior to 100 mm would nominally be in violation of the cease-fire deal.

Ukrainian President Petro Poroshenko on Wednesday condemned reluctance by Russian-backed rebels to pull back their weapons.

But monitors from the OSCE said in its most recent daily report Monday that Ukrainian troops, too, are failing to abide by restrictions on weapons deployments.

“Despite claims that withdrawal of heavy weapons was completed, [monitors] observed the following weapons movements in areas non-compliant with the withdrawal lines: in government-controlled territory, five tanks, three artillery pieces and one Grad Multiple Launch Rocket System," the report said.